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Good viewing distance

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Old Monday 15th July 2019, 16:46   #1
Piskeddu
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Good viewing distance

hello, an information: a Sporting scope at what distance can visualize an animal clearly, I mean that we can understand, for example, that you bird is ... clearly understand that it depends on the optics and the day, but let's say on average . thank you

Giorgio
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Old Tuesday 16th July 2019, 09:13   #2
Troubador
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Giorgio

You need to define your question more clearly.
Do you mean at what distance can you identify the species of bird? This will depend not only on the scope and the distance and the viewing conditions but on what species you are trying to separate. Some species are easier to identify than others. Over the sea you can tell a Kittiwake from its general shape and the way it flies, separating some shearwaters and immature skuas is more difficult. Ducks in some plumages are also difficult, as are many species of wading birds and birds of prey.

Perhaps you mean what is the distance at which you can see all the plumage details but again the distance will be different for an eagle or a falcon or a thrush or a warbler due to the sizes of the birds.

Ciao bella
Lee
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Old Tuesday 16th July 2019, 11:10   #3
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hello Lee, it is a pleasure to hear from you, you are right I expressed myself badly, I meant: optics at what distance can give good identification information (image resolution) taking into account a good optical quality and having a good day to observe. Fortunately, after several years, I get enough and I'm happy to still have a lot to learn, when I go out to watch, I feel good about myself and the world, a hug.

Giorgio
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Old Tuesday 16th July 2019, 14:22   #4
Troubador
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Giorgio
You ask a difficult question because, again, the answer depends on the size of the bird and also depends on the observer knowing what the distance is.

For my recent review of Opticron MM4 77mm scope ( https://www.birdforum.net/showthread.php?t=378770 )
I used a very accurate map of one of the places I used the scope and made marks on it to indicate different distances so that I could make an estimate of the distances some of my observations of birds were made.

At around 400 - 500 metres I could identify a Common Tern with a 20x eyepiece and at around 550 metres I could see the red spot on a Herring Gull's beak with the zoom eyepiece set to 54x.

Of course these observations depended on that scope with those eyepieces and with the viewing conditions on that day and of course my own eyesight. Change any of these and there could be a different answer.

Ciao bella
Lee
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Old Tuesday 16th July 2019, 14:43   #5
Piskeddu
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thanks Lee, you almost answered my terrible question, the last question I ask you is the following: therefore, the limit to be able to see a herring for example, with a good optic / sight / day could be defined as 7/800 meters ? Thank you

Giorgio
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Old Tuesday 16th July 2019, 14:47   #6
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To answer your own question, consider how far away _you_ can identify a particular bird at a given magnification, then extrapolate. A scope view of a bird at 30x will be 3 times larger than the view through 10x bins, so if you can identify a particular bird at 10 meters with your 1x eyes, you should be able to identify it at 100 m using 10x bins, and you should be able to identify it at 300 m using a 30x scope. The only complicating factors in this direct substitution are (1) that the bin allows two eyes versus one with the scope (advantage bins) but the scope should be on a tripod and thus provide a more stable view (advantage scope), and (2) that with additional distance, distorting effects of the atmosphere (e.g. heat shimmer, mirage) can sometimes be a problem, so the scope image might be big but lack detail.

--AP

Last edited by Alexis Powell : Tuesday 16th July 2019 at 14:51.
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Old Tuesday 16th July 2019, 14:57   #7
Piskeddu
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thanks also to you for the comprehensive answer, like Lee's answer.

Giorgio
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Old Tuesday 16th July 2019, 19:29   #8
Troubador
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I think Alexis has given the best answer.

Lee
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Old Tuesday 23rd July 2019, 21:24   #9
lestat
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Don't forget bird identification expertise. I can give the best scope in the world to my mom, but she's clueless on bird id's, so it's either a "insert color" bird or "insert another color" bird :)

But yeah I agree with Alexis' answer.

A question for you Piskeddu, why do you wish to know? Are you considering buying a certain piece of equipment, if so this is not a good point to focus on. Mainly because there's not a clear answer due to the many variations that come into determining a bird. You should focus on other things, but maybe there's another reason why you asked this question?
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Old Wednesday 24th July 2019, 04:47   #10
Piskeddu
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hello, I'm seeing a nest from the balcony of my house, quite far away, Google Maps tells me 1480 meters on a trellis. with the Spotting scope 60x the image degrades a little but it is still very distinguishable, the curiosity was to know to what extent the resolution of the optic and my eye would be able to distinguish the details, intensive that distance.https://uploads.tapatalk-cdn.com/201...503233a258.jpg

Giorgio
https://uploads.tapatalk-cdn.com/201...37c117ff44.jpg

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Old Wednesday 24th July 2019, 09:34   #11
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Piskeddu,
An astronomical telescope such as a Skywatcher 120 ED would be a much better choice at that distance.
100x plus magnification.
Good heavy tripod. AZ4?
Mornings or late afternoon with the sun behind you if possible.
Cloudy conditions may be better.
It was around 35C yesterday, maybe 37C tomorrow, so not good conditions here.
Spring or autumn are best.
Viewing over fields or grass, not concrete or asphalt.
Viewing over water is good.

Regards,
B.
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Old Wednesday 24th July 2019, 09:44   #12
Piskeddu
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hello, I understand, I go around on foot, mountains, lakes and therefore it must also be transportable, I am satisfied with my equipment. the photos were taken with the mobile phone leaning against the eyepiece in the late afternoon around 7pm a week ago.

Giorgio
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Old Wednesday 24th July 2019, 10:16   #13
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Hi Giorgio,

Have a look at 'Horace Dall pocket telescope'.
The 6 inch aperture would probably outperform any normal spotting scope for distance viewing.
He made dozens from 2.5 inch to 6 inch (60mm to 150mm aperture).

The trouble is one would have to make it oneself or get the top optics person to make one.

Regards,
B.
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Old Saturday 27th July 2019, 14:50   #14
etudiant
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Quote:
Originally Posted by Binastro View Post
Hi Giorgio,

Have a look at 'Horace Dall pocket telescope'.
The 6 inch aperture would probably outperform any normal spotting scope for distance viewing.
He made dozens from 2.5 inch to 6 inch (60mm to 150mm aperture).

The trouble is one would have to make it oneself or get the top optics person to make one.

Regards,
B.
That is an impressive bit of smart design!
I'm surprised that no manufacturer has carried it forward, as it seems to offer a unique level of compactness and portability.
Are there any user reports published anywhere?

Last edited by etudiant : Saturday 27th July 2019 at 15:33.
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Old Saturday 27th July 2019, 15:17   #15
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Hi Etudiant,

I think there were reports in ATM and in JBAA amongst others.
But Horace may have started making them about 1930?
I haven't looked for these reports.

The main problem is making the ray tube optics and extremely careful baffling.
This allows their use in daylight.
Horace also routinely aspherised or tuned up the optics, so I am not sure a commercial variant would be cost effective.
His scopes mostly had upright images, even the astro scopes.

Similar designs are used in space telescopes or possibly military versions.

There are some Dall pocket scopes in the Science museum, London.

He took these pocket scopes on cycling trips across Iceland and Lapland where he used dry river beds as his road. Also Patagonia where he met Helena his second wife.
I think he was a widower before that.

He didn't have a car driving licence. He mainly just walked long distances.

Horace made his optics as good as the final product needed to be.
I bought a 90mm short focus refractor. It had HD in pencil on the side of the objective when I cleaned it.
The performance was poor.
I took it to Horace. He said come back in a week.
He told me that it was made as a low power finder for a large scope.
It was made from a large photographic lens he happened to have and the glass had striations.
He refigured it locally and it became a good but not excellent scope. It is O.K. at 100x but not 300x as his best scope would be. He said this was the best he could make it.

He would not take payment, but on my next visit I gave him some Ellore rugs to match the ones he had.

Regards,
B.
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Old Saturday 27th July 2019, 15:54   #16
etudiant
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Quote:
Originally Posted by Binastro View Post
Hi Etudiant,

I think there were reports in ATM and in JBAA amongst others.
But Horace may have started making them about 1930?
I haven't looked for these reports.

The main problem is making the ray tube optics and extremely careful baffling.
This allows their use in daylight.
Horace also routinely aspherised or tuned up the optics, so I am not sure a commercial variant would be cost effective.
His scopes mostly had upright images, even the astro scopes.

Similar designs are used in space telescopes or possibly military versions.

There are some Dall pocket scopes in the Science museum, London.

He took these pocket scopes on cycling trips across Iceland and Lapland where he used dry river beds as his road. Also Patagonia where he met Helena his second wife.
I think he was a widower before that.

He didn't have a car driving licence. He mainly just walked long distances.

Horace made his optics as good as the final product needed to be.
I bought a 90mm short focus refractor. It had HD in pencil on the side of the objective when I cleaned it.
The performance was poor.
I took it to Horace. He said come back in a week.
He told me that it was made as a low power finder for a large scope.
It was made from a large photographic lens he happened to have and the glass had striations.
He refigured it locally and it became a good but not excellent scope. It is O.K. at 100x but not 300x as his best scope would be. He said this was the best he could make it.

He would not take payment, but on my next visit I gave him some Ellore rugs to match the ones he had.

Regards,
B.
Wonderful glimpses of a remarkable man. Thank you!

Aspherics are routine nowadays, so I'd think the Dall scope optics would no longer be prohibitively expensive to make. The mechanical requirements may be an issue, although the spherical secondary should be relatively tolerant of slop.

It just seems astonishing that such a lightweight scope design is not in the market, as I'm sure it would have great appeal to many birders.
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Old Saturday 27th July 2019, 17:19   #17
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Hi,

nobody has yet dared to replicate the mechanics of the pocket telescope which I am sure was adequate for its creator - somebody who can correct defects in an optical instrument with a bit of hand aspherising will only take a minute to get the collimation right after unfolding the pocket telescope.

Might be not so quick for everybody else and thus sth more stable is preferred. Like the Takahashi Mewlon series (small and quite good) or the big Planewave DKs.

PS: here's a nice movie about another side of Horace Dall... doesn't even mention telescopes...

http://sebastiandoerk.com/portfolio/iceland

Joachim

Last edited by jring : Saturday 27th July 2019 at 21:38. Reason: speling
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Old Saturday 27th July 2019, 17:50   #18
etudiant
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Hi,

nobody has yet dared to replicate the mechanics of the pocket telescope which I am sure was adequate for its creator - somebody who can correct defects in an optical instrument with a bot of hand aspherising will only take a minute to get the collimation right after unfolding the pocket telescope.

Might be not so quick for everybody else and thus sth more stable is preferred. Like the Takahashi Mewlon series (small and quite good) or the big Planewave DKs.

PS: here's a nice movie about another side of Horace Dall... doesn't even mention telescopes...

http://sebastiandoerk.com/portfolio/iceland

Joachim
Love the movie, Horace was a tough guy indeed. A remarkable person, would have been a privilege to meet him.

The Takahashi and Planewave offerings seem spectacular, but far from portable, which would be the major attraction of the Dall pocket scope.
So that niche remains unexploited.

It may be that the Dall design could be combined with today's auto focus stabilization techniques to auto collimate. As Jring points out, the instrument performed best for its creator, who knew how to use it most effectively. Ordinary mortals today might well appreciate some electronic crib to get the desired results. Of course that adds cost, complexity and weight, but the basic design leaves lots of margin for that.
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Old Sunday 28th July 2019, 12:07   #19
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100ED picture at 2.8 miles

Here is a picture I took of a local Mt. 2.8 miles,4506 meters away taken with an Orion 100ED Refractor. The original looks a lot better! Also looking through the eyepiece is a lot lot better.
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Old Sunday 28th July 2019, 17:32   #20
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Hi mooreorless,

That is a lovely photo taken on a good day.

Regards,
B.
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Old Sunday 28th July 2019, 18:58   #21
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Hi mooreorless,

That is a lovely photo taken on a good day.

Regards,
B.
Thanks!! Still not as good as looking through eyepiece. I love being up there looking around. Kind of shows what you might see with a scope like that at shorter distance, even just 100mm, of which is excellent indeed.

Last edited by mooreorless : Sunday 28th July 2019 at 19:00.
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